Plane tickets tend to hover at a static mark until they begin to drop at the 105-day mark.

What's the deal with airfare prices? Over the past two years, ticket prices have declined by 3%, while passengers are slammed with checked bag fees (on every major airline except for Southwest, who offers 2 free checked bags) and shrinking legroom (by an order nearly 4 inches over the past few decades), all at the expense of airlines cramming more seats on aircraft for more profits. In short, at the end of the day, the passenger is getting the short end.

But there are ways for the passengers to save on increasingly pricey air travel. You can do the obvious stuff, like book flights that are on a weekday, at an odd hour, or headed to a non-hub airport. You can be diligent in comparing prices through sites like Priceline and CheapAir. And then, of course, there's the well-worn Tuesday trick, which is, simply: Book your flights on a Tuesday. (Airlines typically release sales on Tuesdays, and then end up competing against each other to offer the most enticing price. It's a rare moment where the consumer actually wins, for a change, in this cutthroat market.)

Still, you could take all of these steps and still be missing the most important trick for ensuring cheap airfare. Chances are, you're not booking on the perfect day. According to Jeff Klee, CEO of CheapAir, the perfect day to book airfare is precisely 54 days in advance, on the dot.

In a study from earlier this year, CheapAir analyzed the data of 921 million fares. The company found that between 320 and 106 days before a trip, plane tickets tend to hover at a static price. However, at the 105-day mark, price start dropping, until they reach a nadir at 54 days, before ticking back up. Then, at the 20-day mark, prices dramatically increase.

The folks at CheapAir went on to offer an example of how this can directly benefit the flyer. Using this method, a roughly $400 flight dropped to $344, at 54 days out, before rising to $593. Yes, we did the math for you. That's a whopping 48% overall increase. And once you're on your flight, rest easy: here are the 10 best tricks for sleeping on an airplane.

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